Characterization by optical methods and high-resolution mass spectrometry of the Seine River dissolved organic matter (DOM)

International audienceDissolved organic matter (DOM) is a significant component of freshwaters affecting biogeochemical cycling of metals and water resource. Various inputs (natural and anthropic) in aquatic ecosystems contribute to the chemical complexity and to the variability in composition and reactivity of dissolved organic matter, including fulvic acids (FA). The aim of this study was to describe at a molecular scale the DOM along the Seine Rivers in order to gain insights into its various origins, and chemical characteristics (compositions, structures and reactivity), by means of complementary approaches using optical method measurements (UV-visible spectroscopy and fluorescence spectroscopy) and ESI-FTMS analysis of FA (electro-spray ionisation Fourier Transform mass spectrometry). Results Surface water samples were collected at different sampling point stations of year 2017 between the source and the estuary. The filtrated samples were directly examined by the aforementioned optical methods. FAs were extracted and purified using OASIS HLB resin. Molecular formula of organic molecules constitutive of FA were extracted from ESI(-)-FTMS data. Aromaticity index calculations led to define three classes of FA molecules, namely condensed aromatics, not condensed aromatics and aliphatic-like compounds. Results were discussed in terms of CHONx (x=S, P, Cl) molecules. Molecular compositions were reported in Van Krevelen (VK) diagrams (H/C atomic ratio vs O/C atomic ratio). Identified molecules (~2470), from a sampling point downstream of Paris, are mainly characterized by O/C ratios lower than 0.7. While nitrogen-containing molecules (80%) are found to be present in the trois classes of compounds, phosphorous (8%) and sulfurous (6%) containing molecules fall only in the aliphatic region of VK diagrams. 'CHONPS' molecules (7%) are poorly-oxygenated (O/C